Researchers Link Maternal Instincts, Tots' Smiles

Infants' faces bring about measurable changes in the brains of their mothers.

January 8, 2009, 1:30 AM

July 7, 2008— -- The soft, round cheeks. The dimpled hands that clutch at your finger. The sweet, warm smell of their heads.

Most mothers agree that the sight of their babies can be intoxicating, or even addictive.

A new study explains the neurological roots of maternal bonding -- and may help doctors understand what can sometimes hinder that attachment.

In a study of 28 first-time moms, seeing pictures of their babies' smiles activated parts of the brain involved in rewarding certain behaviors -- such as finding food, water or a mate -- that are vital to the species' survival, says co-author P. Read Montague, a neuroscientist at Baylor College of Medicine in Houston.

These regions of the brain are associated with a signaling hormone called dopamine, Montague says. Mothers looking at their babies smile experience a surge of dopamine -- the same chemical rush that occurs when people use cocaine or nicotine.

The study helps explain how the brain fosters maternal devotion -- and how mothering skills have been passed down through the generations, Montague says.

"This is the mechanism by which you come to be consumed by your baby," Montague says. "All good mothers are addicted to their newborn babies. They will do things above and beyond the call of duty."

Drugs appears to hijack these ancient signaling systems in the brain, making addicts value cocaine or other substances as if they were essential to life, says Lane Strathearn, an assistant professor of pediatrics and co-author of the article, published today in Pediatrics.

In the new study, researchers used functional MRI, or magnetic resonance imaging, to observe the mothers' reactions to their 7-month-old infants. About half the women were breastfeeding.

Strathearn says he hopes his study may help doctors find a way to help women who fail to bond with their babies.

Drug-addicted mothers may not develop normal bonds because other chemicals are providing the reward that should come from nurturing their children, Strathearn says. The brains of women who were abused or neglected as children may be less responsive to stimulation, so that mothering doesn't feel as rewarding as it should.

The study may also shed light on postpartum depression, which affects one in 10 new mothers, says Louann Brizendine, a neuropsychiatrist at the University of California-San Francisco who was not involved in the study. In depressed women, dopamine levels may be too low for women to respond to their babies, Brizendine says. Antidepressants, which replenish dopamine levels, often help these women.

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